Silica-titania, SiO.sub.2. xTiO.sub.2, powders and films have well known commercial applications. Powders have applications as washcoats for the preparation of catalyst substrate materials useful in motor vehicle catalytic converters and the like, since they have been shown to assist in catalytic hydrogenation of CO. In addition, SiO.sub.2.TiO.sub.2 optical films are known to have a high refractive index to provide useful anti-reflective properties suitable for motor vehicle and architectural glazing applications.
Recently, heterometallic alkoxides have been shown to be useful precursors for the preparation of multi-component metal-oxide powders and films via sol-gel processes. A large number of heterometallic alkoxides of the formula [L.sub.m M--(OR).sub.2 --M'L'.sub.n ] are known Mehrotra et al, Mat. Res. Soc. Symp. Proc., 121 (1988) 81; D. C. Bradley et al., Metal Alkoxides, Academic Press, NY, (1978). K. G. Caulton et al., Chem. Rev. 90 (1990) 969. Applicable to the production of SiO.sub.2.TiO.sub.2 films and powders, however, such heterometallic alkoxides of silicon are largely unknown. Moreover, use of such heterometallic alkoxides in CVD for production of multi-component metal-oxide films has generally resulted in the stoichiometry of the metals in the precursor compounds, that is, in the parent alkoxides, not being retained in the resultant films. D. C. Bradley, Chem. Rev. 89 (1989) 1317. As a possible explanation of this loss of stoichiometry, it has been suggested that the heterometallic alkoxide precursors dissociate into component alkoxides of different volatility resulting in the loss of stoichiometry in films.
Known methods of producing SiO.sub.2.xTiO.sub.2 powders and films employ multiple precursor compounds: a first precursor compound as a source of silicon and a second precursor compound as a source of titanium. Maintaining uniformity and/or stoichiometry of SiO.sub.2.TiO.sub.2 throughout the resultant powders and films has proved difficult. The need for exacting control of multiple process parameters to achieve desired stoichiometry and/or uniformity causes increased cost and complexity. Precursors containing silicon and titanium are needed which furnish products in desired forms containing the precursor stoichiometry of silicon and titanium. It is an object of the present invention to provide SiO.sub.2.TiO.sub.2 materials and single source precursor compounds for preparing films and powders of SiO.sub.2.TiO.sub.2 retaining the stoichiometry of the precursers. These and other objects and advantages of the invention will be apparent from the following disclosure.